In the production of hydrocarbons, particularly from production fields offshore, the produced fluids are often transported in underwater pipelines and risers for long distances. The produced fluids normally comprise oil, gas, water and solids. Dependent on the flow rates of the different fluids, it is an aim to reduce the amount of water and/or separate the fluid into different parts prior to transporting the fluids over longer distances in pipelines. It is known for instance to use a one-stage in-line separator to separate liquids and solids from a gas stream before transporting the gas in a pipeline. One example of such separator is shown in WO02/056999.
The separator in WO02/056999 comprises an essentially tubular casing arranged to constitute a part of the actual pipeline. A spin element for rotation of the fluid flow is located at an upstream end of the casing. The outlet means for the gas comprises an outlet element arranged at the downstream end of the casing and having a central, axially extending passage for the gas, and an outer surface which, together with the inner surface of the casing, forms an annulus for the inflow of liquid. A barrier for the liquid is formed at the downstream end of the casing. The outlet means for the liquid comprises an upwards open container arranged at the downstream end of the casing and adapted to receive liquid which flows into the annulus and partly runs down into the container from the bottom area of the casing at the container opening, and partly falls into the container from the area at said barrier.
However, it has proved that the known solutions do not separate the desired amount of liquid from the gas stream. One possible solution to this is to provide two such separators in series; this is however not so favorable as it requires two control systems and each separator induces pressure losses in the gas stream.
It is therefore an object of the present invention to provide a separator and associated method that reduces or alleviates the problems associated with the known solutions mentioned above.
More specifically, an object of the invention is to provide a separator in which the pressure loss in the fluid flowing through the separator is kept at a minimum at the same time as the desired degree of separation is achieved, resulting in a dryer fluid flow, e.g. gas flow, downstream of the separator.